Anything is possible but my first guess is the circuit around MCLR/VPP. During programming, the VPP voltage will rise from 0V to 5V and then up to about 12.5V. It will also go back down to zero several times as part of the programming cycle. As it is connected, when the Pickit takes VPP to zero, C1 and C3 will discharge through D2 and almost certainly prevent the pin reaching the correct voltages.
Try removing D2 and see if it programs correctly. If it does, you need to change the circuit so it complies with Microchip's recommendations around the VPP pin.
Brian.
That proves the capacitors were responsible for the complete loss of communication. It is quite possible that by discharging 10uF into the Pickit3 VPP output has damaged it but there are other possibilities to check first.
Are you powering the PIC from an external 5V supply? If you are relying on the Pickit to provide 5V, are there other devices loading the voltage? Are all supply pins connected? Are there large capacitors across VSS & VDD that the Pickit might struggle to charge up?
Are wires short? Try to keep the connection between the Pickit and PIC as short as possible. The fact that it is reading something suggests a communications error rather than total failure.
If that doesn't help, try connecting PGM as well.
Incidentally, the ID code 00001200 is for the PIC18F4550, is the program properly compiled for the '4520 and not accidentally set to '4550 ?
Brian.
Are there large capacitors across VSS & VDD that the Pickit might struggle to charge up?
Brian.
Everything seems electrically OK but I'm confused over which PIC you are trying to program. Your post title says 18F4520 but now you say it's an 18F4550.
Brian.
Everything seems electrically OK but I'm confused over which PIC you are trying to program. Your post title says 18F4520 but now you say it's an 18F4550.
Brian.
Yes, they must be connected. The programming is actually done by raising VPP to a high voltage (assuming you are not using LV programming mode) then sending serial data bits on PGD synchronized to a clock on PGC. The timing of the data and when it starts relative to VPP rising is critical, that's why Microchip recommend that the programming signals are isolated from other circuitry during the programming procedure.Also Sir can I ask if the supply ground and the PIC Kit3 pin 3 are connected together.
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